Magnetic bearings are bearings that use magnetic force to support a rotor. The advantage of using a magnetic bearing is that there are no mechanical parts to wear out. A disadvantage of magnetic bearings is that they require electrical current to levitate the rotor. At high speeds, eddy currents in the rotor due to different portions of the rotor passing through the magnetic fields of the magnetic actuators can lead to an energy loss.
U.S. Pat. No. 6,191,513 B1 discloses the use of silicon steel laminations to reduce eddy currents that result in power loss due to heating caused by magnetic hysteresis and to a delay in the control of response magnets.
In wafer inspection devices and for electron beam lithography systems for the semiconductor industry commonly use linear stages. However, the time required to scan a wafer with a linear stage is a limit on the wafer throughput for these systems. In the Journal of Vacuum Science and Technology B volume 27, pages 161 through 166 an article by Paul Petric, Chris Bevis, Allen Carroll, Henry Percy, Marek Zywno, Keith Stanford, Alan Brodie, Boah Bareket, and Luca Gralla (hereafter referred to as Petric), a Reflective Electron Beam Lithography (REBL) system is disclosed. It discloses the use of a rotary stage for multiple silicon wafers.